Field of the Invention
This invention relates to piston rings which are for use in internal combustion engines and which have good resistance to friction and wear. Recently, the compression ratio and the revolution speed of internal combustion engines have been considerably increased in order to provide more efficient engine performance. Accordingly, the piston rings used in internal combustion engines are required to have greater wear resistance, so as to withstand the severe conditions of the environment in which they must operate effectively. The degree of wear resistance of piston rings depends upon a number of factors including their ability to resist abrasion, i.e., the grinding abrasive action imparted by solid particles of high hardness, and their ability to resist scuffing. Therefore, in order to enhance the effective wear resistance of piston rings for use in modern internal combustion engines, it as been desirable to improve both the abrasion resistance and the scuffing resistance of such piston rings.